Payment Integration Patterns

Stop guessing at payment integration. This skill gives your agent the production patterns for every payment scenario: one-time charges, subscriptions with trials and dunning, usage-based billing, marketplace split payouts, and cryptocurrency payments.

Covers the full lifecycle that tutorials skip: webhook signature verification, idempotent event handlers, failed payment recovery, subscription state machines, and the security checklist that prevents you from getting hacked or double-charging customers.

Four providers covered:

• Stripe: Checkout, Payment Intents, Subscriptions, Connect (marketplace), metered billing
• PayPal: Server-side integration for international buyers
• Lemon Squeezy: Digital products with automatic tax/VAT handling
• Crypto: USDC on Base with viem, payment matching, and confirmation handling

Includes:

• Complete code examples (JavaScript/TypeScript) for every flow
• Webhook event handling with idempotency patterns
• Dunning sequences for failed payment recovery (10-15% of subscriptions fail)
• Stripe test cards and CLI testing workflow
• Security checklist covering PCI compliance, key management, and signature verification
• Marketplace payout patterns with Stripe Connect
• Usage-based billing with metered subscriptions

Every app needs payments. Most tutorials show the happy path. This skill shows you what breaks in production and how to prevent it.